Shrouded blade arrangement



. Dec. 24, 1968 R. J. ORTOLANO 3,417,964

2 Sheets-Sheet 2 Filed Nov. 20, 1967 United States Patent 3,417,964SHROUDED BLADE ARRANGEMENT Ralph J. Ortolano, Saratoga, Calif., assignorto Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation ofPennsylvania Filed Nov. 20, 1967, Ser. No. 684,124 7 Claims. (Cl. 25377)ABSTRACT OF THE DISCLOSURE This invention provides an improved shroudedblade arrangement of the riveted tenon type for an axial flow elasticfluid utilizing machine such as a turbine or a compressor. The improvedstructure is particularly advantageous when employed in a rotor becauseof its ability to withstand high centrifugal forces without loosening.

The novel feature resides in forming the holes in the shroud with aflared trumpet shape and riveting the tenons to the shroud in such amanner that the tenons are deformed into a flared trumpet shapecomplementary to the shape of the holes and in intimate compressiveabutment therewith.

BACKGROUND OF THE INVENTION Shrouded blade arrangements have beenemployed in the axial flow turbine and compressor art for many years,primarily on the rotors. Typically, the blades are provided withintegral tenon portions which are received in mating holes in the shroudand then riveted to the shroud to make a tight connection therewith. Onesuch arrangement is shown in RI. Ortolano Patent 3,279,751, issued Oct.18, 1966 and assigned to the same assignee as this invention. In thisarrangement, the shroud holes are substantially unchamfered.

Another representative blade shrouding arrangement is shown in A. H.Redding Patent 2,315,655, issued Apr. 6, 1943 and assigned to the sameassignee as this invention. In this arrangement the shroud holes arechamfered to a frusto-conical shape and the tenons are swollen byriveting, into tight and presumably complementary frustoconical shapewith the chamfered portions of the holes.

SUMMARY In accordance with the teachings of this invention,frusto-conical chamfering of the shroud holes results in imperfectriveting of the tenon to the shroud because the tenon does not swell orexpand to a truly frusto-conical shape. Accordingly, the expanded tenondoes not attain a truly tight contiguous relationship with the chamferand small gaps between the outer surface of the tenon and the innersurface of the chamfer are created that eventually may loosen withdamaging results to the rotor blades and/ or the associated statorblades.

The invention provides an improved shrouded blade structure of theriveted type in which the riveted expanded tenon attains a truly tightand contiguous relation with the chamfered portion of the associatedhole in the shroud. This is attained by forming the chamfered portion ofthe hole in the shroud with a flared trumpet shape, i.e., curved convexshape. The natural tendency for a riveted tenon has been discovered toexpand to a flared trumpet shape, hence the resulting riveted connectionis devoid of gaps or spaces between the outer surface of the tenon andthe inner surface of the chamfered portion of the associated hole in theshroud.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view of a portion of ashrouded blade turbine rotor having the invention incorporated therein;

FIG. 2 is an enlarged radial view taken on line II-II 3,417,964 PatentedDec. 24, 1968 of FIG. 1 and showing one of the blades with portions cutaway;

FIG. 3 is a fragmentary plan taken on line IIIIII of FIG. 2 and lookingin the direction of the arrows;

FIG. 4 is a fragmentary view showing a portion of the structure in FIG.2, but before riveting;

FIG. 5 is a fragmentary View similar to FIG. 4, but after riveting;

FIGS. 6 and 7 are views similar to FIGS. 4 and 5, but showing anotherembodiment of the invention;

FIG. 8 is a plan similar to FIG. 3 but showing another embodiment of theinvention in various stages of fabrication;

FIG. 9 is an enlarged sectional view taken on line IXIX of FIG. 8;

FIG. 10 is an enlarged sectional view taken on line X-X of FIG. 8;

FIG. 11 is a view similar to FIG. 10 but showing still anotherembodiment;

FIG. 12 is a fragmentary plan taken on line XIIXII and looking in thedirection of the arrows; and

FIG. 13 is a fragmentary plan illustrating a still further embodiment.

DESCRIPTION OF THE EMBODIMENT SHOWN IN FIGS. 1-5, INCLUSIVE Referring tothe drawings in detail, in FIG. 1 there is shown a portion of a turbinerotor 10 comprising a rotor spindle 11 having an array of radiallyextending blades 12 supported therein and connected to each other insuitable arcuate groups (four per group, as illustrated) by arcuateshroud members 13. Although the entire rotor 10 is not shown, it will beunderstood that the spindle 11 is of circular cross-section and theblades 12 are arranged in an annular array about the rim 14 of thespindle.

The blades 12 may be connected to the rotor rim 14 in any desiredmanner. However, as best illustrated in FIG. 2, the blades are formedwith bulbous T-shaped roots 15 received in a mating peripheral groove 16formed in the spindle rim 14.

The blades are provided with air foil vane portions 17 extendingradially outwardly from the roots 15 and are further provided withtenons 18 extending through uniformly spaced holes 19 formed in theshroud members 13 and secured thereto by deformation of the tenons 18,as by riveting.

As thus far described, the structure is substantially conventional.

The invention comprises a method of manufacture and the resulting tenonand joint structure which will now be described. Since all of the blades12 are substantially identical and are joined to the shroud 13 in thesame manner, only one of the blades will be described.

As best shown in FIG. 4, the tenon 18 is formed integrally with the vaneportion 17 of the blade 12 and of substantially circular cross-section,so that it is initially of substantially cylindrical shape. Theassociated hole 19 in the shroud member 13 is also of circularcross-section but of flared trumpet shape. More particularly, the outersurface 13a of the shroud is chamfered to a depth at least half of itsradial thickness in a manner to provide the hole 19 with an inner wall20 having an arcuate, convex cross sectional surface portion 21. Thewall surface portion 21 defines a circular arc of about having a radiusR at most equal to the thickness T of the shroud 13, but preferablyslightly less than the thickness T. Expressed in another manner, thesurface portion 21 is toroidal in shape, since it may be deemed toinclude the inner quadrant of a torus. Viewed in its entirety the holeis of flared trumpet shape, as previously stated and the tenon 18extends snugly therethrough to a suitable height above the upper surface13a of the shroud.

The tenon 18 is then deformed by riveting blows directed parallel to itscentral axis 22 to secure the blade 17 to the shroud 13 by mutuallycompressive abutment. As viewed in FIG. 5, the deformation of the tenonattained by riveting causes radial swelling and axial shortening of thetenon to provide a preferably flush relation between the tenon 18 andthe shroud surface 13a, but, most importantly the tenon assumes an outerflared trumpet shape 24 exactly concavely complementary to the flaredtrumpet shape of the convex inner wall portion 21 of the hole. It mustbe pointed out that the natural or inherent deforming characteristics ofthe tenon 18 during riveting cause deformation to the flared shape.Hence, after riveting is completed to the degree required for mutuallycompressive relationship of the thus formed joint structure, no voidsbetween the two complementary surfaces are formed which could otherwisecause loosening of the joint structure due to the stresses incurred inoperation.

If desired, after the riveting operation is completed, a peripheral ribportion 25 may be provided on the outer surface of the shroud member 13by machining or otherwise cutting away the portions 26 and 27 of theshroud to the depth indicated by the dot-dash line 13b in FIG. 5.Although a portion of the riveted tenon is also cut away to provide therib 25, the remaining flared portion of the tenon is completely adequateto prevent subsequent loosening of the shroud member 13.

In this embodiment, the shroud member 13 is of rectangular cross-sectionas best seen in FIG. 2, and the tenon 18 extends in a direction normalto the surface 13b.

EMBODIMENT SHOWN IN FIGS. 6 AND 7 FIG. 7 illustrates a completedshrouded blade structure 30 comprising a shroud member 31 and blades 32(only one shown). This structure is similar to the structure shown inFIG. 5 and differs therefrom only in that the shroud member 31 is ofgenerally wedge-shaped crosssection and the blade 33 has an integraltenon 33 whose central axis 34 is normal to the finished outer surface31a of the shroud but inclined with respect to the inner surface 31b ofthe shroud.

FIG. 6 illustrates the above components before riveting of the tenon 33to the shroud member 31. Although the shroud 31 is of wedge-shaped crosssection, and therefore of unsymmetrical cross-sectional shape, the hole34 in the shroud is normal to the unfinished outer surface 310 of theshroud and the flared trumpet shaped wall portion 36 of the hole is ofuniform cross-sectional shape throughout its entire periphery.

Accordingly, here again the tenon 33 is deformed into a shape trulycomplementary to the inner surface of the hole to provide a jointstructure free of voids or gaps between the two complementary surfaces.

EMBODIMENT SHOWN IN FIGS. 8-12, INCLUSIVE FIGS. 11 and 12 illustrate acompleted shrouded blade structure 40 comprising an arcuate shroudmember 41 and blades 42. This structure is similar to the structureshown in FIG. 7 and differs therefrom only in that the tenon 44 and themating hole 44 in the shroud 41 are of non-circular cross section.

FIG. 8 illustrates the shrouded blade structure 40 in various stages offabrication, for ease of comprehension. In this view and in accompanyingFIG. 9, the uppermost blade 42 is illustrated in position in its matinghole before riveting; the next lower blade 42 and the accompanying FIG.10 illustrate the blade after riveting; and below the above two bladesan unbladed opening is illustrated.

The blade 44 is preferably for-med from strip metal of air foil shapeand the tenon 44 is provided by cutting away opposite portions of thestrip metal, thereby to impart a parallelogram cross-section to thetenon.

To accommodate the parallelogram cross section of the tenon 44, themating holes 45 in the shroud member 41 are punched or otherwise cut outto the same parallelogram shape. However, the trumpet shaped flaredportion 47 of the hole 45 is formed in the same manner as in thepreviously described embodiments and during the riveting operation, thetenon 44 is deformed radially to a complementary concave trumpet shapeof circular cross section to completely engage the flared portion 47.Here again the resulting joint structure is truly complementary to theshape of the hole 19 to obviate voids, gaps and irregularities thatcould otherwise lead to loosening of the blade in service.

If desired, after riveting, the shroud 44 may be machined, as previouslydescribed, to provide a peripheral upstanding rib 49.

EMBODIMENT SHOWN -IN FIG. 13

FIG. 13 illustrates a shrouded blade structure 50 similar to the shroudstructure 40 and comprising a blade 51 and a shroud 52 disposed inassembled relation, but before riveting, for clarity. In thisembodiment, the blade 51 is provided with a tenon portion 53 ofgenerally parallelogram cross-section and the shroud 52 is provided witha mating hole 55 of complementary parallelogram shape to receive thetenon 53. However, in this embodiment the flared portion 56 (of theshroud) surrounding the hole 55 is also of complementary parallelogramshape.

In the riveting operation, the tenon 53 is deformed radially to acomplementary shape (not shown) to completely engage the flared portion56 in the same manner as described in connection with the otherembodiments.

Although several embodiments have been shown, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various other changes and modifications without departing from thespirit thereof.

I claim as my invention:

1. A shrouded blade group for an axial fluid flow machine, comprising aplurality of blades having an air foil shaped portion,

each of said blades having a tenon extending from said air foil shapedportion,

an arcuate elongated shroud member having a plurality of longitudinallyspaced holes extending transversely therethrough,

said tenons being received in said holes and rivetedly secured to saidshroud,

said holes being defined by peripheral inner wall surface portions offlared trumpet shape of arcuate convex cross-section, and

said tenons having outer peripheral surface portions of flared trumpetshape of arcuate concave cross-section complementary to said inner wallsurface portions and in intimate compressive abutment therewith.

2. The structure recited in claim 1, wherein the tenons and holes are ofcomplementary non-circular cross-section.

3. The structure recited in claim 1, wherein the cross-sectional shapeof the inner and outer complementary wall surfaces defines an arc of a.circle, and

the tenons, the holes and the flared surface portions are of circularperipheral shape.

4. The structure recited in claim 3, wherein the circular arc is lessthan 5. The structure recited in claim 1, wherein the flared trumpetshape is of circular peripheral configuration, and

the tenons and holes have portions of non-circular peripheralconfiguration.

6. The structure recited in claim 1, wherein the flared trumpet shape isof circular peripheral configuration and has an arcuate cross-sectiondefining an arc of a circle.

7. The structure recited in claim 6, wherein the arc is less than 90 andthe tenons extend through the holes in flush relation with thesurrounding surface of the shroud.

References Cited UNITED STATES PATENTS 2,237,121 4/1941 Stine et al.

FOREIGN PATENTS 344,297 3/ 1931 Great Britain.

EVERETT A. POWELL, JR., Primary Examiner.

